Car manual air conditioning system training platform
Nov 12, 2021
The so-called automobile air-conditioning system refers to a device that can adjust the temperature, humidity, airflow rate, and air cleanliness of the air in the cabin, with the purpose of creating a fresh and comfortable riding environment for the occupants. Its role is not only cooling, but also heating (warm air), ventilating and purifying the air in the car, controlling the humidity of the air in the car, etc. An ideal car air conditioning system can control the temperature in the car at 20-28 The relative humidity is controlled between 50% and 70%, which is the most comfortable temperature and humidity range for the human body. Therefore, the automobile air conditioning system includes four parts: refrigeration device, heating device, air conditioning device and control device. Today's cars are widely used in integrated heating and cooling air-conditioning systems, the layout of which is to assemble the evaporator, heater radiator, centrifugal blower, operating mechanism, etc., called the air conditioner assembly.
Generally speaking, "automobile air conditioner" generally refers to the refrigeration device in the automobile air conditioning system. It is also the device with the most complicated structure and principle and the highest failure rate in the automobile air conditioning system. It is mainly composed of air-conditioning compressors, condensers, evaporators, liquid storage and drying filters (vapor-liquid separators), expansion valves (throttle valves), electronic control systems, air volume distribution systems, refrigerants, refrigerated lubricants, air conditioning pipes Road and other parts of the composition, the following separately talk about their structure and working principle.
Air-conditioning compressor: The air-conditioning compressor is the power source of the automobile air-conditioning system. Its function is to maintain the refrigerant circulating in the refrigeration system at a certain pressure. It sucks in the low-temperature and low-pressure refrigerant vapor from the evaporator and removes it. After compression, the pressure and temperature are increased, and it is sent to the condenser for heat dissipation and temperature reduction.
The air-conditioning compressors used in automobile air-conditioning systems are generally axial piston pumps, which can be divided into two types: fixed pumps and variable pumps. The main difference between them is whether the angle of the swash plate driving the plunger is variable: the swash plate of the fixed pump The angle is fixed, the amount of refrigerant compressed in each cycle is the same, as long as it starts, the power consumption is fixed; the angle of the swash plate of the variable pump can change with the load of the air conditioning system: air conditioning system The load is large, the tilt angle of the swash plate is large, the amount of refrigerant compressed in each cycle is also large, the cooling capacity of the air conditioner is also large, and the power consumption is also large; on the contrary, the load of the air conditioning system is small, the tilt angle of the swash plate is small, and the cooling is compressed in each cycle. The dosage is also small, the cooling capacity of the air conditioner is also small, and the power consumption is also small.
The air conditioner compressor is generally driven by an engine through a belt. There is an electromagnetic clutch at the head of the compressor. When it is energized, the clutch is engaged, which combines the compressor drive shaft with the pulley, drives the swash plate in the compressor to rotate, and causes the plunger to reciprocate to suck and compress the refrigerant , Make it circulate in the system. The fixed-displacement air-conditioning compressor works intermittently, and the electromagnetic clutch controls its working time; while the variable-displacement air-conditioning compressor works continuously, as long as the air-conditioning system is turned on, its electromagnetic clutch is always engaged Yes, adjust the load of the air conditioning system by changing the displacement. Relatively speaking, variable displacement air conditioner compressors have better working smoothness, load can be adjusted continuously, and energy saving effect is better. Therefore, variable displacement compressors are generally used in automatic air conditioning systems used in more advanced vehicles.
Condenser: The role of the condenser is to dissipate the heat of the high-temperature, high-pressure gaseous refrigerant discharged from the air-conditioning compressor to the air outside the car through the condenser, thereby condensing the high-temperature, high-pressure gaseous refrigerant into a higher temperature High-pressure liquid. It is generally installed in the front of the engine water tank, and shares the cooling fan with the engine cooling water tank. In terms of structure, there are three types: tube fin type, tube belt type and parallel flow type.
Evaporator: The function of the evaporator is to boil and vaporize the liquid refrigerant after throttling and depressurization in the evaporator, absorbing the heat of the surrounding air on the surface of the evaporator to cool down, and then the fan blows cold air into the compartment to achieve cooling purpose. The evaporator is generally installed inside the cab's workbench, in terms of structure, there are three types: tube-sheet type, tube-belt type and stacked type.
The condenser and the evaporator are collectively referred to as the heat exchanger of the automobile air conditioning system. The evaporator is responsible for replacing the heat in the car, and the condenser is responsible for dissipating the heat outside the car. Their performance directly affects the refrigeration performance of automobile air conditioners. The requirements for them are fast heat dissipation, large heat dissipation, high efficiency, and small space occupation. Therefore, it is particularly important to keep their surfaces clean. Many car air conditioners have poor refrigeration due to the dirty surfaces and poor heat dissipation of these two devices. Therefore, timely cleaning of impurities outside the condenser and water tank is an important guarantee for the normal operation of the air conditioning system.
Expansion valve (throttle valve): There are now two types of automotive air conditioning refrigeration systems, called expansion valve type and orifice tube type (also called throttle valve type). The main difference between them is the difference in the throttle expansion mechanism. Expansion valve is also called thermal expansion valve. It is installed in front of the evaporator. One of its main functions is throttling. After the high temperature and high pressure liquid refrigerant is throttled through the expansion valve, the volume becomes larger, and the pressure and temperature of the refrigerant are sharp. Decrease; the second is to automatically adjust the flow of refrigerant, so that the refrigerant entering the evaporator is just evaporated in the evaporator. According to different control principles, it can be divided into two types: internal balance and external balance.
The function of the throttle valve is similar to that of the expansion valve. It also uses the throttling effect to increase the volume of the high temperature and high pressure liquid refrigerant after throttling. The pressure and temperature of the refrigerant drop sharply while absorbing a large amount of heat, thereby achieving the purpose of cooling. The difference between it and the expansion valve is that it cannot adjust the flow of refrigerant according to changes in working conditions. It has the advantages of simple structure, low cost, high reliability, energy saving and environmental protection. Therefore, many American and Japanese models have adopted this type of valve. Stream mode. However, in this way, a gas-liquid separator must be installed between the evaporator and the compressor to separate the unevaporated liquid refrigerant and prevent liquid shock to the air-conditioning compressor, thereby ensuring the safe operation of the compressor.
Liquid storage filter drier (vapor-liquid separator): The liquid storage filter drier is generally assembled with the condenser to temporarily store the refrigerant liquefied in the condenser and perform drying and filtering treatments to keep the refrigerant dry and clean. Prevent impurities and dirt in the system from blocking the filter screen and expansion valve, scratching the air conditioning compressor cylinder wall, plunger and bearing, and preventing moisture in the refrigerant from freezing and blocking the expansion valve. Generally, liquid storage filter driers are used in expansion valve refrigeration systems. The vapor-liquid separator is generally used in a throttle-type refrigeration system. Its function is similar to that of a liquid storage filter drier. It also has the function of filtering and drying refrigerant. The main difference is that the liquid storage filter drier is generally installed in the condenser. The vapor-liquid separator is generally installed in front of the air-conditioning compressor to absorb the liquid refrigerant in the refrigerant to prevent liquid shock to the air-conditioning compressor.
Electronic control system: In order to make the car air-conditioning system work normally and maintain the proper temperature and humidity in the cabin, a series of control elements and regulating actuators are required in the system, mainly including temperature controllers, high and low pressure switches, overheat protection switches, Air conditioning amplifiers, air conditioning relays, temperature sensors inside and outside the car, damper servo motors, etc. At present, the air-conditioning control system on automobiles has gradually developed from manual air-conditioning to automatic air-conditioning, and microcomputer automatic control is generally adopted.
According to the complexity of the electronic control system, automobile air conditioning systems can be roughly divided into manual air conditioning and automatic air conditioning. The manual air conditioner can only manually adjust the temperature and air volume of the cold/hot air in a rough grade, and cannot set the specific temperature of the air conditioner in the car. The automatic air-conditioning can be based on the temperature and operating mode set by the driver, the control unit according to the ambient temperature, setting temperature, evaporator outlet temperature, driving conditions and other information, as well as signals input by various sensors, to timely monitor the air supply temperature and air supply speed Make adjustments to keep the air environment in the car at its best. In addition, the automatic air conditioner has a self-checking device, which can automatically find hidden troubles in the air conditioning system and report it to the driver in the form of a fault code.
Air volume distribution system: The air volume distribution system is also known as the air conditioning device of the automobile air conditioning system, which mainly includes the adjustment of the speed of the blower, the adjustment of the inner and outer circulation modes of the air, the adjustment of the air temperature and humidity, the adjustment of the air outlet mode, etc., the main components of the air conditioning device There are blowers, internal and external circulation control valves, temperature control valves, air duct control valves, air-conditioning filter elements, etc. The control methods are pull-wire and motor-driven (currently more motor-driven). They are in line with the control panel of the air conditioner. The switches correspond one to one to control the direction of air flow and the amount of air out.
Refrigerant: Refrigerant is also called refrigeration working fluid, it is the working medium that completes the refrigeration cycle in the refrigeration system. The refrigerant absorbs the heat of the cooled object in the evaporator and evaporates into low-pressure vapor, which is compressed into high-pressure vapor by the compressor, and transfers the heat to the cooling medium (such as air or water) in the condenser to be condensed into liquid, and then is After throttling and pressure reduction, it returns to the evaporator for continuous refrigeration. Therefore, the refrigerant is an important carrier for the energy exchange of the refrigeration device, and the characteristics of the refrigerant play a very important role in the performance of the automobile air conditioning system. Now the commonly used refrigerant in automobile air conditioners is R134a, which is an environmentally friendly refrigerant. Its cooling effect is not as good as R12 (freon), but it does not destroy the ozone layer.
Refrigerated lubricating oil: The lubricating oil used in air-conditioning compressors is called refrigerating lubricating oil or refrigerating machine oil. It is a special lubricating oil that can work normally under high and low temperature conditions. Its main function is to lubricate air-conditioning compression. The surface of machine bearings, pistons and other parts can reduce running resistance and wear, reduce power loss, and extend the service life of parts; second, it has a cooling effect, which almost takes away the heat generated by the friction of the moving surface, and prevents the compressor from overheating. High damage; third, it can penetrate into each friction surface to form an oil seal to prevent refrigerant leakage; fourth, reduce the operating noise of the compressor, constantly wash the friction surface, take away wear debris, and reduce the wear of friction parts.
Air-conditioning pipeline: The function of the air-conditioning pipeline is to flexibly connect the components in the air-conditioning system to form a closed system that can withstand certain vibrations and shocks. It is required to have good sealing performance and certain pressure resistance, and be compatible with refrigerants and refrigerating lubricating oil, and will not corrode or leak due to chemical reactions.
These elements form a closed system, which is filled with refrigerant. The refrigerant circulates under the action of the air-conditioning compressor. It is liquefied from gas to liquid in the condenser of the engine compartment, releasing heat; while in the car, it is liquid. It evaporates into a gaseous state and absorbs heat, thereby reducing the temperature in the car. The above process is repeated repeatedly, so that the temperature in the car is gradually reduced, until the temperature reaches the set temperature, the air-conditioning compressor stops working, the refrigerant no longer flows, and the air-conditioning system stops cooling; when the temperature inside the car rises, the air-conditioning compressor Recombined again to restore refrigeration. This process is repeated to maintain the temperature in the car within the set range. This is the basic refrigeration principle of automobile air conditioning system